Reinforced composite structures have been developed consisting of single or multiple kinds of fibers placed in unidirectional layers or at varying angles or combinations thereof to form a fiber matrix. The matrix is then impregnated with a resin and cured to form a composite structural shape. While these structures are strong "in-plane" that is, in the plane of the fiber layers, they are relatively weak in the vertical direction transverse to the plane of the fiber layers. In this direction there is no mechanical bond between the fibers. The only bond is that formed by the resin impregnation. The most common failure of these structures is delamination of the fiber layers in the vertical direction. Since these structures are often used in aircraft and spacecraft where high strength and low weight construction elements are necessary, such a delamination failure can be catastrophic.
Systems have been devised to form multi fiber composite structures in a three dimensional braided configuration. That is, in addition to the traditional two dimensional layers, the fibers are mechanically interwoven in a three dimensional matrix in the desired cross sectional form. Shapes such as I, H, and L forms can be fabricated as well as other shapes where desired.
While all of the prior art devices are able to produce the desired shapes, the braiding mechanisms are limited in flexibility, complicated and operate at slow speed with many steps in the process being performed manually. Also such machines are not capable of producing large structures required for fabrication of aircraft or spacecraft. Typical of the present machines are those described in U.S. Pat. No. 4,312,261 to Florentine and U.S. Pat. No. 4,719,837 to McKonnell.
In machines of this type to which this invention relates, a horizontal frame forming a carrier plane is provided which is divided in to multiple rows and columns in a rectangular matrix. Carrier members, each holding a supply of fiber on a spool or similar device, are inserted in the rows and columns such that they may be moved in predetermined rectilinear patterns over the carrier plane to form the desired braided form at a fabrication frame situated above the carrier plane. Periodically, the braiding process must be halted in order to compact the braided form. This step is referred to as "beating" and is analogous to the beating step of a conventional fabric loom when weaving two dimensional fabrics.
As the braided form is fabricated, a take-up mechanism above the fabrication plane pulls the completed preform out the top of the machine. As previously described, in the present braiding machines, flexibility of the process has been limited and mechanization has been minimal with many steps being manually performed. In order for three dimensional braided forms to be economically feasible for use in industry, the braiding process must be mechanized to provide for rapid, automated fabrication of composite three dimensional pre-forms.